In a pressurized water reactor, primary coolant led to a reactor is heated by heat energy from fuel assemblies in the reactor and then led to a steam generator. In the steam generator, the heated primary coolant and the secondary coolant are subjected to heat exchange, and the steam generated from the boiling secondary coolant is led to a turbine to be used for power generation.
FIG. 6 is an elevational cross-sectional view schematically illustrating a conventional pressurized water reactor. A reactor pressure vessel 1 is substantially a cylindrical vessel having a vertically-extending axis. The reactor pressure vessel 1 has inlet nozzles 4 through which primary coolant is introduced and outlet nozzles 5 through which heated primary coolant flows out. The reactor pressure vessel 1 has, inside thereof, a large number of fuel assemblies 2, a cylindrical reactor core barrel 3 surrounding the fuel assemblies 2, and a lower core support plate 8 supporting the fuel assemblies 2. An annular downcomer 6 is formed between the reactor pressure vessel 1 and the reactor core barrel 3. Radial keys 9 are installed at a lower portion of the downcomer 6 as radial supports for positioning the reactor pressure vessel 1 in radial directions.
The primary coolant is introduced into the reactor pressure vessel 1 through the inlet nozzles 4 and flows down in the downcomer 6. The primary coolant streams merge in a lower plenum 7 formed below the fuel assemblies 2. The merged primary coolant is then turned 180° and passes upwardly through the lower core support plate 8 and fuel assemblies 2 in the reactor core barrel 3. The primary coolant heated in the fuel assemblies 2 reaches an upper portion of the reactor pressure vessel 1 to be mixed therein, flows out through the outlet nozzles 5, and led to a steam generator (not illustrated).
In such a pressurized water reactor, when a flow rate or a pressure of the primary coolant becomes non-uniform at normal operation time, the fuel assemblies 2 are cooled unevenly. Thus, it is important to supply uniformly-distributed primary coolant to the fuel assemblies 2.
In order to make the coolant flowing through the inlet nozzles uniform in a circumferential direction, there is proposed installation of a streamline shape separation preventing member in the downcomer and formation of radial supports (radial keys) into a streamline shape (Patent Document 1).